Field free region, metastable ions decomposing

Metastable Ions Decomposing in the First Field-Free Region... 

Metastable ions is a term commonly used for ions which decompose unimolecularly in the field-free regions between the analysers, between the source and analyser, or between analyser and detector of ordinary mass spectrometers [186, 421]. These ions typically have lifetimes of the order of microseconds. The lifetimes are determined by the times of flight through the mass spectrometer. The term is used in this review in a broader sense to mean any ions selected according to lifetimes when those lifetimes are of the order of microseconds [i.e. in terms of eqn. (9), i h /us]. 

This analytical field no longer utilizes fragment ions formed in the source, but rather ions characterized with a greater lifetime (> 10 second) and which decompose in the field free regions (FFR) of the mass spectrometer. These ions are termed metastable ions and are quite useful for demonstrating the existence of characteristic uni-molecular (or bimolecular) decompositions. 

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